New method to prepare very stable and biocompatible fluorescent silica nanoparticles

Bioactive silica nanoparticles target autophagy, NF-κB, and MAPK pathways to inhibit osteoclastogenesis

Spherical 50 nm silica-based nanoparticles (SiNPs) promote healthy bone homeostasis and maintenance by supporting bone forming osteoblast lineage cells while simultaneously inhibiting the differentiation of bone resorbing osteoclasts. Previous work demonstrated that an intraperitoneal injection of SiNPs in healthy mice - both young and old - increased bone density and quality, suggesting the possibility that SiNPs represent a dual action therapeutic. However, the underlying mechanisms governing the osteoclast response to SiNPs have yet to be fully explored and defined. Therefore, the goals of this study were to investigate the cellular and molecular mechanisms by which SiNPs inhibit osteoclastogenesis. SiNPs strongly inhibited RANKL-induced osteoclast differentiation within the first hours and concomitantly inhibited early transcriptional regulators such as Nfatc1. SiNPs simultaneously stimulated expression of autophagy related genes p62 and LC3β dependent on ERK1/2 signaling pathway. Intriguingly, SiNPs were found to stimulate autophagosome formation while inhibiting the autophagic flux necessary for RANKL-stimulated osteoclast differentiation, resulting in the inhibition of both the canonical and non-canonical NF-κB signaling pathways and stabilizing TRAF3. These results suggest a model in which SiNPs inhibit osteoclastogenesis by inhibiting the autophagic machinery and RANKL-dependent functionality. This mechanism of action defines a novel therapeutic strategy for inhibiting osteoclastogenesis.

Synthesis and Characterization of Alkoxysilane-Bearing Photoreversible Cinnamic Side Groups: A Promising Building-Block for the Design of Multifunctional Silica Nanoparticles

The present study reports on the synthesis of a new alkoxysilane-bearing light-responsive cinnamyl group and its application as a surface functionalization agent for the development of SiO₂ nanoparticles (NPs) with photoreversible tails. In detail, cinnamic acid (CINN) was activated with N-hydroxysuccinimide (NHS) to obtain the corresponding NHS-ester (CINN-NHS). Subsequently, the amine group of 3-aminopropyltriethoxysilane (APTES) was acylated with CINN-NHS leading to the generation of a novel organosilane, CINN-APTES, which was then exploited for decorating SiO₂ NPs. The covalent bond to the silica surface was confirmed by solid state NMR, whereas thermogravimetric analysis unveiled a functionalization degree much higher compared to that achieved by a conventional double-step post-grafting procedure. In light of these intriguing results, the strategy was successfully extended to naturally occurring sepiolite fibers, widely employed as fillers in technological applications. Finally, a preliminary proof of concept of the photoreversibility of the obtained SiO₂@CINN-APTES system has been carried out through UV diffuse reflectance. The overall outcomes prove the consistency and the versatility of the methodological protocol adopted, which appears promising for the design of hybrid NPs to be employed as building blocks for photoresponsive materials with the ability to change their molecular structure and subsequent properties when exposed to different light stimuli.

One-Pot Bifunctionalization of Silica Nanoparticles Conjugated with Bioorthogonal Linkers: Application in Dual-modal Imaging

Covalent surface modification of silica nanoparticles (SNPs) offers great potential for the development of multimodal nanomaterials for biomedical applications. Herein, we report the synthesis of covalently conjugated bifunctional SNPs and...

Matching the Cellulose/Silica Films Surface Properties for Design of Biomaterials That Modulate Extracellular Matrix

The surface properties of composite films are important to know for many applications from the industrial domain to the medical domain. The physical and chemical characteristics of film/membrane surfaces are totally different from those of the bulk due to the surface segregation of the low surface energy components. Thus, the surfaces of cellulose acetate/silica composite films are analyzed in order to obtain information on the morphology, topography and wettability through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle investigations. The studied composite films present different surface properties depending on the tetraethyl orthosilicate (TEOS) content from the casting solutions. Up to a content of 1.5 wt.% TEOS, the surface roughness and hydrophobicity increase, after which there is a decrease in these parameters. This behavior suggests that up to a critical amount of TEOS, the results are influenced by the morphology and topographical features, after which a major role seems to be played by surface chemistry-increasing the oxygenation surfaces. The morphological and chemical details and also the hydrophobicity/hydrophilicity characteristics are discussed in the attempt to design biological surfaces with optimal wettability properties and possibility of application in tissue engineering.

Carminic Acid Linked to Silica Nanoparticles as Pigment/Antioxidant Bifunctional Excipient for Pharmaceutical Emulsions

The incorporation of pigments and natural polyphenols into inorganic matrices, resulting in a hybrid material that improves the resistance and chemical stability of the pigments and the antioxidant capacity of the materials, has been of great interest to the pharmaceutical, chemical and food industries. The aim of this work was to prepare and characterize a bifunctional pigment-antioxidant nanomaterial-based carminic acid-decorated solid core-mesoporous shell silica nanoparticles, evaluating its properties as a pigment, its antioxidant capacity and its properties as a chemical stabilizer of emulsions. The chemical stability of oil-in-water (O/W) Pickering emulsions was evaluated determining the stability of vitamin E solubilized in the oil phase. Carminic acid was attached through the action of coupling ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) agents, and the resulting spherical and homogeneous nanoparticles showed a diameter close to 175 nm. A notorious change of emulsion color was observed by the addition of the nanomaterial. Emulsions showed an attractive pink color, and when the pH was adjusted to pH 3 and pH 9, a change in color was observed, analogous to carminic acid in solution. The nanomaterial incorporation also improved chemical stability, decreasing vitamin E consumption to 9.26% of the initial value, demonstrating an important antioxidant effect of the developed nanomaterial.

Impact of the chemical nature and position of spacers on controlling the optical properties of silicon quantum dots

The unique properties of silicon quantum dots (SQDs), including intriguing optical properties, biocompatibility, and ease of surface modification have made them excellent candidates for a variety of optoelectronic and biomedical applications. Unfortunately, the low quantum efficiency (QE), unstable photoluminescence, and poor colloidal stability of SQDs have hindered their wide applicability. Herein, we report the synthesis of four assemblies of SQDs (1.6-1.8 nm average diameter) functionalized with fluorescein dye through isothiocyanate (-NCS) and carboxylate (COO-) spacers in the benzene ring of the fluorescein to produce the dyads Am-SQD-Fl, DiAm-SQD-Fl, urea-SQD-Fl, and SQD-Fl. The photophysical measurements showed that the spacer played a key role in directing and controlling the optical properties of SQDs dyads, with the isothiocyanate spacer leading to a significant improvement in the QE of the dyad systems up to 65% and extending their photostability for at least one year. The interactions between the SQDs and fluorescein in the dyads Am-SQD-Fl, DiAm-SQD-Fl, and SQD-Fl were found to mainly proceed through photoinduced electron transfer at different rates, while energy transfer was confirmed to be the predominant process in the dyad urea-SQD-Fl. To demonstrate the suitability of the functionalized SQDs for bioimaging applications, the water-soluble dyads were examined for fluorescence imaging of human bone cancerous U2OS cells.

Classification, Synthesis, and Application of Luminescent Silica Nanoparticles: a Review

Luminescent materials are of worldwide interest because of their unique optical properties. Silica, which is transparent to light, is an ideal matrix for luminescent materials. Luminescent silica nanoparticles (LSNs) have broad applications because of their enhanced chemical and thermal stability. Silica spheres of various sizes could be synthesized by different methods to satisfy specific requirements. Diverse luminescent dyes have potential for different applications. Subject to many factors such as quenchers, their performance was not quite satisfying. This review thus discusses the development of LSNs including their classification, synthesis, and application. It is the highlight that how silica improves the properties of luminescent dye and what role silica plays in the system. Further, their applications in biology, display, and sensors are also described.

Detection of Ampicillin-Resistant E. coli Using Novel Nanoprobe-Combined Fluorescence In Situ Hybridization

Antibiotic-resistant bacteria present a global threat because the infections they cause are difficult to treat. Therefore, it is highly important to develop advanced methods for the identification of antibiotic resistance gene in the virulent bacteria. Here, we report the development of novel nanoprobes for fluorescence in situ hybridization (FISH) and the application of the nanoprobe to the detection of ampicillin-resistant Escherichia coli. The nanoprobe for FISH was synthesized by the modified sol-gel chemistry and the synthesized nanoprobe provided strong fluorescent signals and pH stability even under natural light condition. For the double-identification of bacteria species and ampicillin-resistance with a single probe in situ, the nanoprobes were conjugated to the two kinds of biotinylated probe DNAs; one for E. coli-species specific gene and the other for a drug-resistant gene. By using the nanoprobe-DNA conjugants, we successfully detected the ampicillin-resistant E. coli through the FISH technique. This result suggests the new insight into light stable FISH application of the nanoprobe for a pathogenic antibiotic-resistance bacterium.

Silica-Based Organic-Inorganic Hybrid Fluorescent Ink for Security Applications

A facile formulation of fast-drying fluorescent ink made from nanostructured fluorescent silica nanocrystals is presented. The rheostable viscous ink suitable for screen printing was developed by careful selection of organic vehicle components, which was later printed onto various rigid and flexible substrates. Photoluminescence studies of the printed film confirmed that the formulated ink composition did not show noticeable influence on the excitation property of the fluorescent silica. The developed cost-effective and fast-curing fluorescent silica ink with desirable luminescent property makes it a suitable candidate for information encryption, optical devices, and energy conversion applications.

Antioxidant Nanomaterial Based on Core⁻Shell Silica Nanospheres with Surface-Bound Caffeic Acid: A Promising Vehicle for Oxidation-Sensitive Drugs

The design of efficient, biocompatible, and easily prepared vehicles for drug delivery is a subject of great interest for medicine and pharmaceutical sciences. To achieve the above goals, surface functionalization is critical. Here, we report a hybrid nanocarrier consisting of core⁻shell silica nanospheres and the antioxidant caffeic acid linked to the surface, to evaluate their in vitro antioxidant capacity, their capability to protect oxidation-sensitive compounds incorporated in nanoparticles, and to study the interaction with bovine serum albumin protein. The results show that the radical-scavenging activity of immobilized caffeic acid is attenuated in the silica nanospheres; however, other antioxidant properties such as Fe2+-chelating activity and singlet oxygen quenching are enhanced. In addition, caffeic acid is protected from binding to proteins by the nanoparticle, suggesting that this nanosystem is more likely to maintain the antioxidant activity of caffeic acid in biological media. Finally, the natural antioxidant barrier on the nanocarrier is able to delay the degradation of a compound incorporated into this nanovehicle. Considering all findings, this work proposes a suitable tool for pharmaceutical and cosmetic industries as an antioxidant nanocarrier for oxidation-sensitive drugs.

Interactions between Metal Oxides and Biomolecules: from Fundamental Understanding to Applications

Metallo-oxide (MO)-based bioinorganic nanocomposites promise unique structures, physicochemical properties, and novel biochemical functionalities, and within the past decade, investment in research on materials such as ZnO, TiO₂, SiO₂, and GeO₂ has significantly increased. Besides traditional approaches, the synthesis, shaping, structural patterning, and postprocessing chemical functionalization of the materials surface is inspired by strategies which mimic processes in nature. Would such materials deliver new technologies? Answering this question requires the merging of historical knowledge and current research from different fields of science. Practically, we need an effective defragmentation of the research area. From our perspective, the superficial accounting of material properties, chemistry of the surfaces, and the behavior of biomolecules next to such surfaces is a problem. This is particularly of concern when we wish to bridge between technologies in vitro and biotechnologies in vivo. Further, besides the potential practical technological efficiency and advantages such materials might exhibit, we have to consider the wider long-term implications of material stability and toxicity. In this contribution, we present a critical review of recent advances in the chemistry and engineering of MO-based biocomposites, highlighting the role of interactions at the interface and the techniques by which these can be studied. At the end of the article, we outline the challenges which hamper progress in research and extrapolate to developing and promising directions including additive manufacturing and synthetic biology that could benefit from molecular level understanding of interactions occurring between inanimate (abiotic) and living (biotic) materials.

Three-dimensional direct visualization of silica dispersion in polymer-based composites

We present a novel strategy for realizing the three-dimensional direct visualization of silica dispersion by the fluorescence modification of a silica filler.

Synthesis of pH stable, blue light-emitting diode-excited, fluorescent silica nanoparticles and effects on cell behavior

To date, delivery of light-emitting diode (LED)-activated compounds to cells and tissue remains a challenge. Silica-based materials possess good biocompatibility and have advantages of control of size and shape. Fluorescent silica nanoparticles (NPs) have been synthesized and used for applications such as cell tracking and tumor identification. Here, we report the synthesis and optimization of fluorescent silica NPs, which incorporate a naphthalimide dye with triethoxysilanes that are excited by the blue LED wavelength (LEDex NPs). The NPs can be imaged in the 420-470 nm wavelength, demonstrate a high quantum yield, are stable in a range of pH, and are taken into the cells. Therefore, these NPs represent a novel imaging technology for biomedical applications.

Ultrabright Fluorescent Silica Nanoparticles Embedded with Conjugated Oligomers and Their Application in Latent Fingerprint Detection

Fluorescent micro- and nanosized particles have a broad range of applications in biology, medicine, and engineering. For these uses, the materials should have high emission efficiency and good photostability. However, many organic fluorophores suffer from aggregation-induced quenching effects and photobleaching. Here, we used a simple method based on covalently blending a fluorescent conjugated oligomer with silica nanoparticles to achieve emission quantum yields as high as 97%. The resulting system also showed excellent stability under continuous light illumination, in a range of pH values and temperatures, and in common solvents. This fluorescent material showed outstanding properties, including highly efficient blue emission, low cost, low toxicity, and easy synthesis. Furthermore, its effectiveness for latent fingerprint detection was demonstrated as a proof of concept on various substrates. The obtained emissive fingerprint powder gave good optical/fluorescent images with high contrast and resolution between the ridges and spaces.

The stimulatory effect of silica nanoparticles on osteogenic differentiation of human mesenchymal stem cells

Silica-based materials with favourable biocompatibility are generally considered as excellent candidates for applications in biomedical fields. However, previous researches mainly focused on the safety of silica-based materials, their effects on osteogenic differentiation of human mesenchymal stem cells (hMSCs) still need further investigations. In this study, core-shell fluorescent silica nanoparticles (silica NPs) with three different sizes (S1 ~ 50 nm, S2 ~ 200 nm, S3 ~ 400 nm, respectively) were prepared according to the Stöber method. The silica NPs with different sizes did not affect the cell viability (even up to a concentration of 500 µg ml^-1), showing size- and dose-independent cytocompatibility of silica NPs on hMSCs. Uptake of silica NPs significantly enhanced the activity of alkaline phosphatase (ALP) and the formation of bone-like nodules of hMSCs after osteogenic induction. At the concentration of 10 µg ml^-1, after treating hMSCs with larger sized silica NPs (S2 and S3), higher ALP activity of hMSCs was measured and larger sized bone-like nodules were formed by hMSCs compared with that treated with smaller sized silica NPs (S1).The enhanced osteogenic potential of hMSCs treated with silica NPs may be attributed to the Si released from silica NPs due to the lysosomal degradation inside hMSCs. These results demonstrate the stimulatory effect of silica NPs on osteogenic differentiation of hMSCs and the application potential of silica NPs in bone tissue engineering.

Synthesis and stability of IR-820 and FITC doped silica nanoparticles

Fluorescent silica nanoparticles (NPs) have potential in biomedical applications as diagnostics and traceable drug delivery agents. In this study, we have synthesized fluorescent dye grafted silica NPs in two step process. First, a stable method to synthesize various sizes of silica NPs ranging from 20 to 52, 95, 210 and 410nm have been successfully demonstrated. Secondly, as-synthesized silica NPs are readily grafted with some fluorescent dyes like IR-820 and fluorescein isothiocyanate (FITC) dyes by simple impregnation method. IR-820 and FITC dyes are 'activated' by (3-mercaptopropyl)trimethoxysilane (MPTMS) and (3-aminopropyl)triethoxysilane (APTS) respectively prior to the grafting on silica NPs. UV-vis spectroscopy is used to test the stability of dye grafted silica NPs. The fluorescent dye grafted silica NPs are quite stable in aqueous solution. Also, a new type of dual dye-doped hybrid silica nanoparticles has been developed. The combination of microscopic and spectroscopic techniques shows that the synthesis parameters have significant effects on the particle shape and size and is tuneable from a few nanometers to a few hundred nanometers. The ability to create size controlled nanoparticles with associated (optical) functionality may have significant importance in bio-medical imaging.

Functional regeneration of the transected recurrent laryngeal nerve using a collagen scaffold loaded with laminin and laminin-binding BDNF and GDNF

Recurrent laryngeal nerve (RLN) injury remains a challenge due to the lack of effective treatments. In this study, we established a new drug delivery system consisting of a tube of Heal-All Oral Cavity Repair Membrane loaded with laminin and neurotrophic factors and tested its ability to promote functional recovery following RLN injury. We created recombinant fusion proteins consisting of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) fused to laminin-binding domains (LBDs) in order to prevent neurotrophin diffusion. LBD-BDNF, LBD-GDNF, and laminin were injected into a collagen tube that was fitted to the ends of the transected RLN in rats. Functional recovery was assessed 4, 8, and 12 weeks after injury. Although vocal fold movement was not restored until 12 weeks after injury, animals treated with the collagen tube loaded with laminin, LBD-BDNF and LBD-GDNF showed improved recovery in vocalisation, arytenoid cartilage angles, compound muscle action potentials and regenerated fibre area compared to animals treated by autologous nerve grafting (p < 0.05). These results demonstrate the drug delivery system induced nerve regeneration following RLN transection that was superior to that induced by autologus nerve grafting. It may have potential applications in nerve regeneration of RLN transection injury.

Rapid Imaging of Latent Fingerprints Using Biocompatible Fluorescent Silica Nanoparticles

Fluorescent silica nanoparticles (FSNPs) are synthesized through the Stöber method by incorporating silane-modified organic dye molecules. The modified fluorescent organic dye molecule is able to be prepared by allylation and hydrosilylation reactions. The optical properties of as-prepared FSNPs are shown the similar optical properties of PR254A (allylated Pigment Red 254) and have outstanding photostability. The polyvinylpyrrolidone (PVP) is introduced onto the surface of FSNP to enhance the binding affinity of PVP-coated FSNP for latent fingerprints (LFPs) detection. The simple preparation and easy control of surface properties of FSNPs show potential as a fluorescent labeling material for enhanced latent fingerprint detection on hydrophilic and hydrophobic substrates in forensic science for individual identification.

Boronate Affinity Fluorescent Nanoparticles for Förster Resonance Energy Transfer Inhibition Assay of cis-Diol Biomolecules

Förster resonance energy transfer (FRET) has been essential for many applications, in which an appropriate donor-acceptor pair is the key. Traditional dye-to-dye combinations remain the working horses but are rather nonspecifically susceptive to environmental factors (such as ionic strength, pH, oxygen, etc.). Besides, to obtain desired selectivity, functionalization of the donor or acceptor is essential but usually tedious. Herein, we present fluorescent poly(m-aminophenylboronic acid) nanoparticles (poly(mAPBA) NPs) synthesized via a simple procedure and demonstrate a FRET scheme with suppressed environmental effects for the selective sensing of cis-diol biomolecules. The NPs exhibited stable fluorescence properties, resistance to environmental factors, and a Förster distance comparable size, making them ideal donor for FRET applications. By using poly(mAPBA) NPs and adenosine 5'-monophosphate modified graphene oxide (AMP-GO) as a donor and an acceptor, respectively, an environmental effects-suppressed boronate affinity-mediated FRET system was established. The fluorescence of poly(mAPBA) NPs was quenched by AMP-GO while it was restored when a competing cis-diol compounds was present. The FRET system exhibited excellent selectivity and improved sensitivity toward cis-diol compounds. Quantitative inhibition assay of glucose in human serum was demonstrated. As many cis-diol compounds such as sugars and glycoproteins are biologically and clinically significant, the FRET scheme presented herein could find more promising applications.

Observation of a Flowing Duct in the Abdominal Wall by Using Nanoparticles

The primo vascular system (PVS) is being established as a circulatory system that corresponds to acupuncture meridians. There have been two critical questions in making the PVS accepted as a novel liquid flowing system. The first one was directly to show the flow of liquid in PVS and the second one was to explain why it was not observed in the conventional histological study of animal tissues. Flow in the PVS in the abdominal cavity was previously verified by injecting Alcian blue into a primo node. However, the tracing of the dye to other subsystems of the PVS has not been done. In the current work we injected fluorescent nanoparticles (FNPs) into a primo node and traced them along a primo vessel which was inside a fat tissue in the abdominal wall. Linea alba is a white middle line in the abdominal skin of a mammal and a band of fat tissue is located in parallel to the linea alba in the parietal side of the abdominal wall of a rat. In this fat band a primo vessel runs parallel to the prominent blood vessels in the fat band and is located just inside the parietal peritoneum. About the second question on the reason why the PVS was not in conventional histological study the current work provided the answer. Histological analysis with hematoxyline and eosine, Masson’s trichrome, and Toluidine blue could not discriminate the primo vessel even when we knew the location of the PVS by the trace of the FNPs. This clearly explains why the PVS is hard to observe in conventional histology: it is not a matter of resolution but the contrast. The PVS has very similar structure to the connective tissues that surround the PVS. In the current work we propose a method to find the PVS: Observation of mast cell distribution with toluidine blue staining and the PN has a high density of mast cells, while the lymph node has low density.

Conjugation of A and B Blood Group Structures to Silica Microparticles for the Detection of Antigen-Specific B Cells

Silica microparticles were functionalized with A and B blood group carbohydrate antigens (A type I, A type II, B type I, and B type II) to enable the detection and monitoring of ABO antigen-specific B cells. Microparticles were prepared via the Stöber synthesis, labeled with an Alexafluor fluorescent dye, and characterized via TEM and fluorescence microscopy. The silica microparticles were functionalized with (3-aminopropyl)trimethoxysilane (APTMS), followed by the use of an established fluorenylmethyloxycarbonyl (Fmoc)-protected PEG-based linker. The terminal Fmoc moiety of the PEG-based linker was then deprotected, yielding free amino groups, to which the A and B antigens were coupled. The carbohydrate antigens were synthesized with a p-nitrophenol ester to enable conjugation to the functionalized silica microparticles via an amide bond. The number of free amine groups available for coupling for a given mass of PEG-functionalized silica microparticles was quantified via reaction with Fmoc-glycine. The antigen-functionalized microparticles were then evaluated for their specificity in binding to A and B antigen-reactive B-cells via flow cytometry, and for blocking of naturally occurring antibodies in human serum. Selective binding of the functionalized microparticles to blood group-reactive B cells was observed by flow cytometry and fluorescence microscopy. The modular approach outlined here is applicable to the preparation of silica microparticles containing any carbohydrate antigen and alternative fluorophores or labels. This approach therefore comprises a novel, general platform for screening B cell populations for binding to carbohydrate antigens, including, in this case, the human A and B blood group antigens.

Realizing both selective adsorption and efficient regeneration using adsorbents with photo-regulated molecular gates

A new generation of adsorbents possessing photo-regulated molecular gates were fabricated and consequently, realized selective adsorption and efficient desorption simultaneously.

Nano-hydroxyapatite modulates osteoblast lineage commitment by stimulation of DNA methylation and regulation of gene expression

Hydroxyapatite (HA) is the primary structural component of the skeleton and dentition. Under biological conditions, HA does not occur spontaneously and therefore must be actively synthesized by mineralizing cells such as osteoblasts. The mechanism(s) by which HA is actively synthesized by cells and deposited to create a mineralized matrix are not fully understood and the consequences of mineralization on cell function are even less well understood. HA can be chemically synthesized (HAp) and is therefore currently being investigated as a promising therapeutic biomaterial for use as a functional scaffold and implant coating for skeletal repair and dental applications. Here we investigated the biological effects of nano-HAp (10 × 100 nm) on the lineage commitment and differentiation of bone forming osteoblasts. Exposure of early stage differentiating osteoblasts resulted in dramatic and sustained changes in gene expression, both increased and decreased, whereas later stage osteoblasts were much less responsive. Analysis of the promoter region one of the most responsive genes, alkaline phosphatase, identified the stimulation of DNA methylation following cell exposure to nano-HAp. Collectively, the results reveal the novel epigenetic regulation of cell function by nano-HAp which has significant implication on lineage determination as well as identifying a novel potential therapeutic use of nanomaterials.

Glutathione- and pH-responsive nonporous silica prodrug nanoparticles for controlled release and cancer therapy

A myriad of drug delivery systems such as liposomes, micelles, polymers and inorganic nanoparticles (NPs) have been developed for cancer therapy. Very few of them, however, have the ability to integrate multiple functionalities such as specific delivery, high circulation stability, controllable release and good biocompatibility and biodegradability in a single system to improve the therapeutic efficacy. Herein, we report two types of stimuli-responsive nonporous silica prodrug NPs towards this goal for controlled release of anticancer drugs and efficient combinatorial cancer therapy. As a proof of concept, anticancer drugs camptothecin (CPT) and doxorubicin (DOX) were covalently encapsulated into silica matrices through glutathione (GSH)-responsive disulfide and pH-responsive hydrazone bonds, respectively, resulting in NPs with sizes tunable in the range of 50-200 nm. Both silica prodrug NPs showed stimuli-responsive controlled release upon exposure to a GSH-rich or acidic environment, resulting in improved anticancer efficacy. Notably, two prodrug NPs simultaneously taken up by HeLa cells showed a remarkable combinatorial efficacy compared to free drug pairs. These results suggest that the stimuli-responsive silica prodrug NPs are promising anticancer drug carriers for efficient cancer therapy.

Bioactive silica nanoparticles reverse age-associated bone loss in mice

We recently reported that in vitro, engineered 50nm spherical silica nanoparticles promote the differentiation and activity of bone building osteoblasts but suppress bone-resorbing osteoclasts. Furthermore, these nanoparticles promote bone accretion in young mice in vivo. We have now investigated the capacity of these nanoparticles to reverse bone loss in aged mice, a model of human senile osteoporosis. Aged mice received nanoparticles weekly and bone mineral density (BMD), bone structure, and bone turnover were quantified. Our data revealed a significant increase in BMD, bone volume, and biochemical markers of bone formation. Biochemical and histological examinations failed to identify any abnormalities caused by nanoparticle administration. Our studies demonstrate that silica nanoparticles effectively blunt and reverse age-associated bone loss in mice by a mechanism involving promotion of bone formation. The data suggest that osteogenic silica nanoparticles may be a safe and effective therapeutic for counteracting age-associated bone loss.

FROM THE CLINICAL EDITOR

Osteoporosis poses a significant problem in the society. Based on their previous in-vitro findings, the authors' group investigated the effects of spherical silica nanoparticles in reversing bone loss in a mouse model of osteoporosis. The results showed that intra-peritoneal injections of silica nanoparticles could increase bone mineral density, with little observed toxic side effects. This novel method may prove important in future therapy for combating osteoporosis.

Synthesis of fluorescent dye-doped silica nanoparticles for target-cell-specific delivery and intracellular microRNA imaging

MicroRNA (miRNA) is found to be up-regulated in many kinds of cancer and therefore is classified as an oncomiR. Herein, we design a multifunctional fluorescent nanoprobe (FSiNP-AS/MB) with the AS1411 aptamer and a molecular beacon (MB) co-immobilized on the surface of the fluorescent dye-doped silica nanoparticles (FSiNPs) for target-cell-specific delivery and intracellular miRNA imaging. The FSiNPs were prepared by a facile reverse microemulsion method from tetraethoxysilane and silane derivatized coumarin that was previously synthesized by click chemistry. The as-prepared FSiNPs possess uniform size distribution, good optical stability and biocompatibility. In addition, there is a remarkable affinity interaction between the AS1411 aptamer and the nucleolin protein on the cancer cell surface. Thus, a target-cell-specific delivery system by the FSiNP-AS/MB is proposed for effectively transferring a MB into the cancer cells to recognize the target miRNA. Using miRNA-21 in MCF-7 cells (a human breast cancer cell line) as a model, the proposed multifunctional nanosystems not only allow target-cell-specific delivery with the binding affinity of AS1411, but also can track simultaneously the transfected cells and detect intracellular miRNA in situ. The proposed multifunctional nanosystems are a promising platform for a highly sensitive luminescent nonviral vector in biomedical and clinical research.

Fluorescent silica nanoparticles modified chemically with terbium complexes as potential bioimaging probes: their fluorescence and colloidal properties in water

Highly fluorescent silica nanoparticles were synthesized using silylated terbium complexes, which were prepared easily through formation of a Schiff base.

Bioactive silica nanoparticles promote osteoblast differentiation through stimulation of autophagy and direct association with LC3 and p62

We recently identified an engineered bioactive silica-based nanoparticle formulation (designated herein as NP1) that stimulates in vitro differentiation and mineralization of osteoblasts, the cells responsible for bone formation, and increases bone mineral density in young mice in vivo. The results demonstrate that these nanoparticles have intrinsic biological activity; however, the intracellular fate and a complete understanding of the mechanism(s) involved remains to be elucidated. Here we investigated the cellular mechanism(s) by which NP1 stimulates differentiation and mineralization of osteoblasts. We show that NP1 enters the cells through a caveolae-mediated endocytosis followed by stimulation of the mitogen activated protein kinase ERK1/2 (p44/p42). Our findings further revealed that NP1 stimulates autophagy including the processing of LC3β-I to LC3β-II, a key protein involved in autophagosome formation, which is dependent on ERK1/2 signaling. Using a variant of NP1 with cobalt ferrite magnetic metal core (NP1-MNP) to pull down associated proteins, we found direct binding of LC3β and p62, two key proteins involved in autophagosome formation, with silica nanoparticles. Interestingly, NP1 specifically interacts with the active and autophagosome associated form of LC3β (LC3β-II). Taken together, the stimulation of autophagy and associated signaling suggests a cellular mechanism for the stimulatory effects of silica nanoparticles on osteoblast differentiation and mineralization.

Rational design of phosphorescent chemodosimeter for reaction-based one- and two-photon and time-resolved luminescent imaging of biothiols in living cells

A selective phosphorescent biothiols probe is synthesized based on Ir(III) complex 1, which has 2,2'-biquinoline as the N^N ligand for realizing the satisfied two-photon absorption cross-section and two-functionalized 2-phenylpyridine ligands with an α,β-unsaturated ketone moiety as the thiol reaction site. The one- and two-photon optical properties of 1 are investigated through UV-vis absorption spectrum and photoluminescence spectrum. This Ir(III) complex can act as an excellent one- and two-photon excited "OFF-ON" phosphorescent probe for biothiols based on the 1,4-addition of biothiol to α,β-unsaturated ketones. Moreover, one- and two-photon-induced luminescent imagings of biothiols in living cells are also realized. Furthermore, the experiments of time-resolved photoluminescence technique and fluorescence lifetime imaging microscopy demonstrate that 1 is able to detect biothiols in the presence of strong background fluorescence. In addition, probe 1 is adsorbed into the shell of mesoporous silica nanoparticles with core-shell structure to form a nanoprobe, which can realize the ratiometric detection of biothiols in absolute water solution and living cells based on two phosphorescent signals.

Bio-active engineered 50 nm silica nanoparticles with bone anabolic activity: therapeutic index, effective concentration, and cytotoxicity profile in vitro

Silica-based nanomaterials are generally considered to be excellent candidates for therapeutic applications particularly related to skeletal metabolism however the current data surrounding the safety of silica based nanomaterials is conflicting. This may be due to differences in size, shape, incorporation of composite materials, surface properties, as well as the presence of contaminants following synthesis. In this study we performed extensive in vitro safety profiling of ∼ 50 nm spherical silica nanoparticles with OH-terminated or Polyethylene Glycol decorated surface, with and without a magnetic core, and synthesized by the Stöber method. Nineteen different cell lines representing all major organ types were used to investigate an in vitro lethal concentration (LC) and results revealed little toxicity in any cell type analyzed. To calculate an in vitro therapeutic index we quantified the effective concentration at 50% response (EC50) for nanoparticle-stimulated mineral deposition activity using primary bone marrow stromal cells (BMSCs). The EC50 for BMSCs was not substantially altered by surface or magnetic core. The calculated Inhibitory concentration 50% (IC50) for pre-osteoclasts was similar to the osteoblastic cells. These results demonstrate the pharmacological potential of certain silica-based nanomaterial formulations for use in treating bone diseases based on a favorable in vitro therapeutic index.

Volume labeling with Alexa Fluor dyes and surface functionalization of highly sensitive fluorescent silica (SiO2) nanoparticles

A new synthesis approach is described that allows the direct incorporation of fluorescent labels into the volume or body of SiO2 nanoparticles. In this process, fluorescent Alexa Fluor dyes with different emission wavelengths were covalently incorporated into the SiO2 nanoparticles during their formation by the hydrolysis of tetraethoxysilane. The dye molecules were homogeneously distributed throughout the SiO2 nanoparticles. The quantum yields of the Alexa Fluor volume-labeled SiO2 nanoparticles were much higher than nanoparticles labeled using conventional organic dyes. The size of the resulting nanoparticles was controlled using microemulsion reaction media with sizes in the range of 20-100 nm and a polydispersity of <15%. In comparison with conventional surface tagged particles created by post-synthesis modification, this process maintains the physical and surface chemical properties that have the most pronounced effect on colloidal stability and interactions with their surroundings. These volume-labeled nanoparticles have proven to be extremely robust, showing excellent signal strength, negligible photobleaching, and minimal loss of functional organic components. The native or "free" surface of the volume-labeled particles can be altered to achieve a specific surface functionality without altering fluorescence. Their utility was demonstrated for visualizing the association of surface-modified fluorescent particles with cultured macrophages. Differences in particle agglomeration and cell association were clearly associated with differences in observed nanoparticle toxicity. The capacity to maintain particle fluorescence while making significant changes to surface chemistry makes these particles extremely versatile and useful for studies of particle agglomeration, uptake, and transport in environmental and biological systems.

LONG-TERM MONITORING OF THE PHYSICOCHEMICAL PROPERTIES OF SILICA-BASED NANOPARTICLES ON THE RATE OF ENDOCYTOSIS AND EXOCYTOSIS AND CONSEQUENCES OF CELL DIVISION

Nanomaterials are diverse in size, shape and charge and these differences likely alter their physicochemical properties in biological systems. We have investigated how these properties alter the initial and long-term dynamics of endocytosis, cell viability, cell division, exocytosis, and interaction with a collagen extracellular matrix using silica-based fluorescent nanoparticles and the murine pre-osteoblast cell line, MC3T3-E1. Three surface modified nanoparticles were analyzed: positively charged (PTMA), negatively charged (OH), and neutrally charged polyethylene glycol (PEG). Positively charged PTMA-modified nanoparticles demonstrated the most rapid uptake, within 2 hours, while PEG modified and negatively charged OH nanoparticles demonstrated slower uptake. Cell viability was >80% irrespective of nanoparticle surface charge suggesting a general lack of toxicity. Long-term monitoring of fluorescent intensity revealed that nanoparticles were passed to daughter cells during mitotic cell division with a corresponding decrease in fluorescent intensity. These data suggest that irrespective of surface charge silica nanoparticles have the potential to internalize into osteoblasts, albeit with different kinetics. Furthermore, long lived nanoparticles have the potential to be transferred to daughter cells during mitosis and can be maintained for weeks intracellularly or within a collagen matrix without toxicity and limited exocytosis.

Mesenchymal stem cells as delivery vehicle of porphyrin loaded nanoparticles: effective photoinduced in vitro killing of osteosarcoma

Mesenchymal stem cells (MSC) have the unique ability to home and engraft in tumor stroma. These features render them potentially a very useful tool as targeted delivery vehicles which can deliver therapeutic drugs to the tumor stroma. In the present study, we investigate whether fluorescent core-shell PMMA nanoparticles (FNPs) post-loaded with a photosensitizer, namely meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) and uploaded by MSC could trigger osteosarcoma (OS) cell death in vitro upon specific photoactivation. In co-culture studies we demonstrate using laser confocal microscopy and time lapse imaging, that only after laser irradiation MSC loaded with photosensitizer-coated fluorescent NPs (TPPS@FNPs) undergo cell death and release reactive oxygen species (ROS) which are sufficient to trigger cell death of all OS cells in the culture. These results encourage further studies aimed at proving the efficacy of this novel tri-component system for PDT applications.

Size-dependent tumor penetration and in vivo efficacy of monodisperse drug-silica nanoconjugates

The size of a nanomedicine strongly correlates with its biodistribution, tissue penetration, and cell uptake. However, there is limited understanding how the size of nanomedicine impacts the overall antitumor efficacy. We designed and synthesized camptothecin-silica nanoconjugates (Cpt-NCs) with monodisperse particle sizes of 50 and 200 nm, two representative sizes commonly used in drug delivery, and evaluated their antitumor efficacy in murine tumor models. Our studies revealed that the 50 nm Cpt-NC showed higher anticancer efficacy than the larger analogue, due presumably to its faster cellular internalization and more efficient tumor accumulation and penetration. Our findings suggest that nanomedicine with smaller sizes holds great promise for improved cancer therapy.

Effect of colloidal silica on the spectral behaviour of 7-hydroxycoumarin in aqueous medium

Absorption and emission spectroscopic studies, in combination with FTIR measurements, were carried out for 7-hydroxycoumarin (7HC) and nanocolloidal dispersion of silica. Attempt has been made to identify the characteristics of excited state H-bond formed between colloidal silica and 7HC in aqueous medium. Both the absorption and emission spectra of 7HC was found to be dependent on the concentration of silica. At lower silica concentrations, the absorption spectra decreases with increasing silica concentration, on the other hand, at higher concentration a bathochromic shift occurs in the absorption spectra of 7HC. Fluorescence behaviour followed the opposite trend in comparison to the absorption spectra. It is proposed that at lower silica concentration, excited state H-bond was formed between 7HC and silica dispersions. At higher concentration, the decrease in fluorescence intensity is attributed to the self quenching of adsorbed dye molecules over silica surface following the mechanism of Homo Förster resonance energy transfer (HFRET). Results were correlated with the size and surface charge of colloidal silica as measured by dynamic light scattering and zeta potential studies.

Perylenediimide functionalized bridged-siloxane nanoparticles for bulk heterojunction organic photovoltaics

Perylenediimide functionalized bridged siloxane nanoparticles were prepared by direct hydrolysis and condensation of a perylenediimide silane precursor in the presence of a catalytic amount of tetraethoxysilane (TEOS). The sizes of the particles were controlled by adjusting organotrialkoxysilane, base, and TEOS concentrations. Using this modified Stöber method, we were able to incorporate a higher load of organic content (∼70%) into the siloxane core compared to typical organically modified Stöber silica nanoparticles. The size, shape, and surface morphology of these functionalized particles were visualized using transmission electron microscopy. Their compositions were confirmed by FTIR, thermogravimetric analysis, and elemental analysis. The photovoltaic performance of these nanohybrids in the poly(3-hexylthiophene) polymer matrix was evaluated. The device made from a sample annealed at 150 °C showed reasonably good photovoltaic performance with a power conversion efficiency of 1.56% under standard test conditions of AM 1.5G spectra at an illumination intensity of 100 mW cm(-2).

Synthesis and biological response of size-specific, monodisperse drug-silica nanoconjugates

Drug-containing nanoparticles (NPs) with monodisperse, controlled particle sizes are highly desirable for drug delivery. Accumulating evidence suggests that NPs with sizes less than 50 nm demonstrate superior performance in vitro and in vivo. However, it is difficult to fabricate monodisperse, drug-containing NPs with discrete sizes required for studying and characterizing existing relationships among particle size, biologic processing, and therapeutic functionality. Here, we report a scalable process of fabricating drug-silica conjugated nanoparticles, termed drug-silica nanoconjugates (drug-NCs), which possess monodisperse size distributions and desirable particle sizes as small as 20 nm. We find that 20 nm NCs are superior to their 50 and 200 nm NC analogues by 2-5- and 10-20-fold, respectively, with regard to tumor accumulation and penetration and cellular internalization. These fundamental findings underscore the importance and necessity of further miniaturizing nanomedicine size for optimized drug delivery applications.